1. Field of the Disclosure
This invention relates generally to multi-parallel hydrocyclone separators for use in downhole applications for separating multi-phase mixtures. More specifically, this invention relates to multi-parallel hydrocyclone separators for use in downhole applications for separating oil and water in a production flow from a subterranean hydrocarbon reservoir.
2. Background Art
Many oil wells produce hydrocarbons with high percentage of water and require systems to separate water from hydrocarbons. In typical practice, a produced mixture is lifted to the surface and the water is separated from the hydrocarbon in a surface processing station for subsequent water discharge into the environment. There is significant energy wastage and increased operating costs associated with transporting downhole fluids to the surface processing station for separation.
Hydrocyclones, which are compact, centrifugal separators, separate components of a mixture according to the relative densities of the components. For example, hydrocyclones may be used to separate solids, liquids, and gases. Similarly, hydrocyclones may be used to separate different components in a fluid mixture, for example oils and water, based on different densities. Hydrocyclones are widely used in both onshore and offshore oil production in above-ground applications, such as bulk water knockout from production fluids, or for downhole de-oiling produced water prior to water reinjection into a formation or water disposal to a disposal site.
Hydrocyclone separators are able to continuously separate a production fluid into a heavy phase and a light phase using centrifugal forces created when a production liquid stream is provided into a conically shaped cyclone at a high speed in a substantially tangential direction. The liquid swirls around the inside of the hydrocyclone at a high speed to create a centrifugal force on the liquid. Typically, hydrocyclones are designed to provide a centrifugal force that is much greater, perhaps several hundred folds greater, than the gravitational force on the liquid, such that the effects of gravity on the liquid are negligible. Under these conditions, the heavy liquid is forced to the outer wall of the hydrocyclone, thereby forcing the light phase liquid toward the center of the hydrocyclone. The heavier phase moving along the wall of the conical hydrocyclone will migrate towards the end with the small diameter (the tail), while the lighter phase in the center will be pushed towards the end with the larger diameter (the head).
The use of hydrocyclones to separate oil and water from the production flow of an oil well is well known. Downhole oil/water separation technology enables separation of oil and water in the well bore, wherein the oil-enriched fluid is transported to the surface and the water-enriched fluid may be injected back into a formation above or below the production zone without being transported to the surface.
Hydrocyclones may include bulk oil/water separators designed to operate on mixtures with a relatively high concentration of oil in water; pre-de-oiler separators designed to separate oil from a mixture with a lower concentration of oil (for example the water and oil mixture discharged from a bulk oil/water separator); and de-oiler separators designed to separate oil from a mixture containing a relatively low concentration of oil in water in order to discharge substantially clean water into the environment.
Hydrocyclone separators typically require connecting multiple hydrocyclones in parallel in order to achieve significant flow rates. On surface, multiple (sometimes dozens) of hydrocyclone separators may be connected to a single manifold, which evenly splits the flow to each hydrocyclone. However, this approach is not practical in a downhole tool due to space limitation.
When packaging hydrocyclones for downhole applications, space constraints require that a novel approach be taken to assemble hydrocyclones in the limited space. There have been a number of prior proposals for hydrocyclone separation systems for use in downhole operations. Generally, such systems comprise an outer tubular housing dimensioned to fit within a casing of an oil well. The housing provides a supporting structure for securing a plurality of hydrocyclones therein. Complex piping within the housing communicates with the outlets of the hydrocyclones so that the separated water can be re-injected into the environment, and an oil-rich mixture resulting from the removal of water may be transported to the surface.
For example, U.S. Pat. No. 6,627,081, issued to Hilditch et al. discloses a hydrocyclone assembly having multiple hydrocyclones disposed in a housing, wherein the outlets of hydrocyclones are connected via connecting unions to overflow and underflow passages in the housing. The multiple hydrocyclones may be arranged in opposite orientation to maximize the utilization of the limited space.
When packaging multiple hydrocyclones for downhole applications, managing various flows into and out of hydrocyclone separation systems is critical. This may involve properly managing the additive fluid velocities coming from multiple hydrocyclones to prevent erosion and properly balance the input to each hydrocyclone. There is still a need for better hydrocyclone separation assemblies for downhole use.